.\" Copyright (c) 1983, 1993.\"	The Regents of the University of California.  All rights reserved..\".\" Redistribution and use in source and binary forms, with or without.\" modification, are permitted provided that the following conditions.\" are met:.\" 1. Redistributions of source code must retain the above copyright.\"    notice, this list of conditions and the following disclaimer..\" 2. Redistributions in binary form must reproduce the above copyright.\"    notice, this list of conditions and the following disclaimer in the.\"    documentation and/or other materials provided with the distribution..\" 3. All advertising materials mentioning features or use of this software.\"    must display the following acknowledgement:.\"	This product includes software developed by the University of.\"	California, Berkeley and its contributors..\" 4. Neither the name of the University nor the names of its contributors.\"    may be used to endorse or promote products derived from this software.\"    without specific prior written permission..\".\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION).\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF.\" SUCH DAMAGE..\".\"	@(#)3.t	8.1 (Berkeley) 6/8/93.\".NH 1Access control.PPThe printer system maintains protected spooling areas so thatusers cannot circumvent printer accounting orremove files other than their own.The strategy used to maintain protectedspooling areas is as follows:.IP \(bu 3The spooling area is writable only by a \fIdaemon\fP userand \fIdaemon\fP group..IP \(bu 3The \fIlpr\fP program runs set-user-id to \fIroot\fP andset-group-id to group \fIdaemon\fP.  The \fIroot\fP access permitsreading any file required. Accessibility is verifiedwith an \fIaccess\fP\|(2) call.  The group IDis used in setting up proper ownership of filesin the spooling area for \fIlprm\fP..IP \(bu 3Control files in a spooling area are made with \fIdaemon\fPownership and group ownership \fIdaemon\fP.  Their mode is 0660.This insures control files are not modified by a userand that no user can remove files except through \fIlprm\fP..IP \(bu 3The spooling programs,\fIlpd\fP, \fIlpq\fP, and \fIlprm\fP run set-user-id to \fIroot\fPand set-group-id to group \fIdaemon\fP to access spool files and printers..IP \(bu 3The printer server, \fIlpd\fP,uses the same verification procedures as \fIrshd\fP\|(8C)in authenticating remote clients.  The host on which a clientresides must be present in the file /etc/hosts.equiv or /etc/hosts.lpd andthe request message must come from a reserved port number..PPIn practice, none of \fIlpd\fP, \fIlpq\fP, or\fIlprm\fP would have to run as user \fIroot\fP if remotespooling were not supported.  In previous incarnations ofthe printer system \fIlpd\fP ran set-user-id to \fIdaemon\fP,set-group-id to group \fIspooling\fP, and \fIlpq\fP and \fIlprm\fP ranset-group-id to group \fIspooling\fP.